This invention relates generally to aircraft capable of combined rotary wing and fixed wing flight and, more particularly, to apparatus for controlling movement of the rotor blades of such aircraft.
Rotor/wing aircraft such as the aircraft disclosed in U.S. Pat. No. 5,454,530 titled "Canard Rotor/Wing" are capable of operation in both a helicopter and a fixed-wing mode of flight. In order to achieve this dual mode flight, a rotor/wing aircraft is equipped with a rotating hub, similar to the rotating hub of a helicopter, to which are attached a plurality of rotor blades extending radially outward from the hub. In the first flight regime the hub and rotor blades are rotated in a manner similar to that of a helicopter. This enables the aircraft to move vertically, hover, and fly translationally at relatively slow speeds. In the second flight regime, the rotor is locked with the rotor blades positioned to operate as fixed wings, thereby enabling the aircraft to fly at relatively high speeds configured as a conventional fixed-wing aircraft.
In order to enable a rotor/wing aircraft to operate in the helicopter mode, the blades of the rotor/wing must be free to rotate about their respective pitch axes in response to the control inputs. As with a conventional helicopter, the longitudinal and lateral rotor blade cyclic pitch control as well as the average rotor blade pitch (collective) are transmitted to the rotor blades by means of a rotor blade swashplate mechanism. Flight control inputs are translated into elevation and tilt angle of the swashplate which are transmitted to the rotor blades by means of pitch links attached to the leading or trailing edges of the blades. For purposes of this disclosure, however, a two-bladed rotor with pitch links connected to the leading edges of the blades will be addressed specifically.
In order for the rotor/wing aircraft to operate in fixed wing mode, the rotor blades must be locked into a rigid assembly preferably having substantially uniform bilateral response to the aerodynamic forces encountered during fixed wing flight. It should be noted that, although in helicopter mode the pitch link of each blade is at the aerodynamic leading edge of the blade, in fixed wing mode one rotor blade stops on the port side of the aircraft and one rotor blade stops on the starboard side. By definition, if the aircraft is moving forward, one rotor blade will have airflow in the opposite direction during fixed wing flight than the airflow in helicopter mode. Thus, the leading edge of one helicopter blade becomes a trailing edge in fixed wing flight. Accordingly, although one of the helicopter blade pitch links will be at the leading edge of one half of the wing, the other pitch link will be at the trailing edge of the other half of the wing.
Although it would be theoretically possible to create a rigid wing by securing the pitch links of each of the rotor blades, to do so would result in an aircraft of less than optimum stability because one blade would be locked in position by a leading edge link and the other blade by a trailing edge link. Accordingly, what is needed is an apparatus for locking both rotor blades of a rotor/wing aircraft to form a rigid wing having a uniform bilateral aerodynamic response.